Today, a manufacture line of a semiconductor device or flat panel display (FPD) employs a single type process for processing target substrates (semiconductor wafers, glass substrates, etc.) one by one. Specifically, recently, in order to promote consistency, connectivity, or complexity of processes, a multi single type inline process system where a plurality of process units are integrally arranged along or around a transfer path of a transfer system is being widely used.
Such a transfer system for a single type process unit or for a multi single type inline process system uses a single type substrate transfer apparatus which holds substrates one by one, and carries the substrates into or out of each process unit one by one. Generally, such a type of substrate transfer apparatus is configured as a transfer robot, and includes one or several transfer arms capable of holding substrates to face upward one by one and performing rotating motion, elevating movement, and advancing and retreating movement.
The transfer arm of such a substrate transfer apparatus includes a substrate holding portion (holder or holding mechanism) that prevents a substrate from being misaligned or from falling during transfer. For such a conventional type of substrate holding portion, a rear surface friction method, a taper pad method, a dropping method, or a vacuum adhesion method is used.
In the rear surface friction method, a plurality of holding pads having a plate or block shape are discretely attached to a top surface or holding surface of the transfer arm. Then, the substrate is placed on the holding pad to face upward, and is held by using a frictional force between a rear surface of the substrate and a pad surface (for example, refer to FIG. 8 and descriptions thereof in Patent Reference 1). Elastomer, ceramic, or the like is used as a material of such a holding pad.
In the taper pad method, a plurality of holding pads having a tapered side surface (having a trapezoid longitudinal section) are discretely attached to a holding surface of the transfer arm at predetermined intervals such as to surround the substrate. Then, a periphery portion of the substrate is fastened to the tapered side surface of the holding pads such that the substrate is held facing upward (for example, refer to FIG. 4 and descriptions thereof in Patent Reference 1). According to this method, the substrate is dropped along the tapered side surface from a location higher than a top surface of the holding pad, above the holding surface of the transfer arm, and thus the substrate is held in line-contact to a location on the tapered side surface where gravity of the substrate and a reaction from the holding pad are balanced.
In the dropping method, a pick portion of the transfer arm is formed as a fork slightly larger than an outline shape of the substrate along the outline shape of the substrate, and a plurality of claw portions protruding from and extending inward the fork to surround the substrate at predetermined intervals adhere to the fork. Then, the substrate is dropped down to a bottom surface (holding surface) of the claw portions along an inclined surface formed on an inner side of the claw portions, so as to hold the substrate facing upward in surface-contact at the bottom surface of the claw portion (for example, refer to FIG. 4 and descriptions thereof in Patent Reference 2).
In the vacuum adsorption method, a plurality of suction holes are provided on a holding surface of the transfer arm, a rear surface of the substrate is placed on the suction holes, and a vacuum suction apparatus connected to the suction holes through an air passage performs vacuum suction, thereby fixing the substrate to the transfer arm at the suction holes (for example, refer to FIG. 3 and descriptions thereof in Patent Reference 2).